Distributed caching with centralized control

The benefits of using caches for reducing traffic in backbone trunk links and for improving web access times are well-known. However, there are some known problems with traditional web caching, namely, maintaining freshness of web objects, balancing load among a number of caches and providing protection against cache failure. This paper investigates in detail the advantages and disadvantages of a distributed architecture of caches which are coordinated through a central controller. In particular, the performance of a set of independent caches is compared against the performance of a set of coordinated distributed caches using extensive simulation. The conclusion is that a distributed architecture of coordinated caches consistently provides a better hit ratio, improves response time, provides better freshness, achieves load balancing, and increases the overall traffic handling capacity of a network while paying a small price in terms of additional control traffic. In particular, we have observed up to 40% improvement in hit ratio, 70% improvement in response time, 60% improvement in freshness and 25% improvement in traffic handling capacity of a network with caches.